1. Field of the Invention
The present invention relates to an image processing system having an interface function for data transfer with external equipment.
2. Related Background Art
In recent years, color copying machines have progressed remarkably in their development and availability. In addition, such color copying machines have come to incorporate various types of printer engines, such as an ink-jet type, a thermal ink-transfer type, a silver-salt photography type and an electrophotography type. Among these, the use of the electrophotography type, with its advantageous capabilities of achieving high speed and high image quality, has spread remarkably. An example of a conventional color copying machine is shown in FIG. 1.
In this color copying machine, a color original is subjected to color separation with respect to each pixel thereof, and is read in a digital manner in the form of an electrical signal. Then, in a color laser beam printer section employing an electrophotographic process, a full-color print image is obtained. The machine is roughly divided into two sections, namely, an image reading section A and an image printing section B.
In the image reading section A, an original exposure lamp 2 illuminates a color original 1. Light reflected from, and thus indicative of, the color original 1 is focused onto a color image sensor 3, forming an image thereon. The color image sensor 3 performs a color separation with respect to each pixel, and produces a color-separate color image signal. The color image signal is processed by a color signal processing circuit 4, transmitted through a cable 25, and input to an image processing circuit 5. The image processing circuit 5 digitizes the input signal, subjects the digitized color signal to digital image processing, performs color correction, and then supplies a digital image signal to the image printing section B.
When image data is sent to the image printing section B via a cable 6, a semiconductor laser drive section 7 modulates a semiconductor laser 8 on the basis of the image data. Then, a color-separate one-color latent image is formed in a raster pattern on a photosensitive drum (latent image formation). The latent image thus formed is visualized by a developing device 21 (development), thereby forming a color-separate toner image on the photosensitive drum. A sheet of copying paper is fed from a cassette 17 or a cassette 18, and wound on a transfer drum 12, on which synchronized motion of the paper and the color-separate toner image causes the toner image to be transferred to the copying paper (transfer).
As will be clearly understood from FIG. 1, an image corresponding to only one color is formed by executing the image forming process one time. Therefore, the process of subjecting the original to color separation has to be executed the same number of times as the number of the toner colors, that is, four times in correspondence with yellow (Y), magenta (M), cyan (C) and black (K). Similarly, in synchronism with the color separation for each color, the process comprising latent image formation, development and transfer has to be executed in correspondence with each of the color components. Thus, when the copying paper wound on the transfer drum 12 has rotated four times until the completion of four transfer operations for four colors, the paper is separated from the drum 12 by a separation pawl 13. Then, the copying paper is guided to heat-pressure fixing rollers 15 and 16, by which the toner image on the copying paper is fixed. Thereafter, the paper is discharged to the outside of the copying machine, thereby completing the production of a full-color copy. In this way, with such a color copying machine, the image forming process must be performed a plurality of times in order to prepare a plurality of color-separate images Y, M, C and K of the stated colors. This feature of the machine renders it unsuitable for achieving a speed higher than the currently available level.
In view of the above-described point, a certain type of apparatus has been proposed. Such an apparatus includes a memory for storing color image signals, and four drums for Y, M, C and K. Image forming operations for Y, M, C and K are performed in a mutually overlapping relationship in time, thereby achieving a higher speed.
On the other hand, an apparatus of the same type as that shown in FIG. 1 can be adapted, utilizing the characteristic of digitally handling images possessed by this type of apparatus, to input image data via an interface circuit from external equipment, thereby enabling various processings. Proposals for such apparatuses have been made, for example, in U.S. Ser. No. 691,968, filed Apr. 26, 1991.
However, it has not been possible to realize an efficient and simple structure for providing an interface of the above-described kind for an apparatus, such as above, having an image memory as well as a plurality of drums.
It is a great problem to determine how to construct the interface when it is to be provided in the type of apparatus having a color image memory, in particular, a memory for storing compressed color image data (such an apparatus may not necessarily have a plurality of drums).
Another problem arises from the variety of forms in which a set of data expresses a color image. The data may be in the form of a set comprising red (R), green (G) and blue (B), or M, C, Y and K. Still alternatively, the data may be formulated according to the (L, a*, b*) system or the (X, Y, Z) system. Thus, the form of the data varies depending on the type of the equipment used. However, in a conventional color copying apparatus having an interface function, since the output section (printer) is capable of receiving only data in the form of M, C, Y and K, the equipment (such as a host computer, not shown) which is to supply the output section with color image data may have to operate on a large amount of color image data to effect conversion such as (R, G, B).fwdarw.(C, M, Y, K). Such conversion requires a relatively long period of time. For example, when 96M byte image data is converted for a full-color A3 image, a period of several tens of seconds to several minutes is necessary.